No, I'm not going to try the new 2x TC. But regarding your question whether one could expect it to perform better: That's a tough one!
My opinion, Wout: I don't think the mediocre performance with TC was the TC's fault. I think the 1.7x magnification clearly shows the limits of this zoom - or almost any zoom to be fair.
If you have a look at the latest test of the "old" VRI here at photozone, you can see how bad that lens looked with TCs. Even with a 1.4x the center performance drops from "very good" to "good" and border-performance from "very good" to "poor" at f/4.0 (similar picture at f/5.6) - with the TC 1.7x naturally even worse.
And that was although with a TC you don't even "see" the real border/corner-performance of the lens but need only a smaller image circle due to the magnification.

I think you need a real good fixed focal to enjoy a TC...
(unfortunately the Nikon TC will not work with my Sigma fixed focals )

You can find the new review at Photozone here:
http://www.photozone.de/nikon_ff/511-nikkorafs7020028vr2ffUnfortunately no tests with TC yet: "This review initially does not contain measurements with TCs, but these will follow at a later date (including the new TC-20E III)."
The verdict: highly recommended, optical quality 4* (out of 5)!

No. Unfortunately they didn't follow up on their promise...
Plus, I haven't found any other lab-test with comparable targets.
So, yep: Camera Labs seems the only source for this kind of information on one of Nikon's premier zooms